1. Field of the Invention
This invention relates to a method for shape modification of a polishing pad for polishing a workpiece, particularly a wafer into a desired surface shape.
2. Description of the Related Art
Conventionally, a polishing apparatus (CMP apparatus) by the chemical mechanical polishing method (CMP method) has been used for polishing and planarizing a workpiece such as a wafer. The CMP apparatus generally includes a polishing plate for polishing a wafer and a polishing head for holding a wafer, and a wafer is polished by pressing the wafer held by the polishing head against the polishing plate and rotating the wafer and the polishing plate while supplying a polishing agent (slurry) between the above two.
Here, a polishing pad is attached to the surface of this polishing plate for polishing a wafer, and the wafer is pressed against this polishing pad and polished. However, since the polishing amount of this polishing pad decreases due to the clogging of the surface and the like, the polishing pad is dressed after polishing a few wafers in the CMP apparatus.
Since a polishing pad is polished on the surface little by little as dressed, the surface shape changes and the flatness tends to gradually deteriorate. When a wafer is polished by using such a polishing pad, a disadvantage is that the wafer cannot be planarized stably with a high degree of accuracy.
Therefore, conventionally, an operator measured the flatness of a polishing pad surface upon performing a dressing, analyzed the polishing amount from the measurement result, and adjusted the dressing.
However, the conventional method of manually measuring the flatness of a polishing pad surface by an operator has a disadvantage of requiring a great amount of time in the measuring operation and being inefficient. Moreover, even though the flatness of a polishing pad itself is adjusted, a variation occurs in the flatness of the polishing pad in a state of being attached to a polishing plate due to the difference between apparatus of the polishing plates where the pad is attached.
In order to solve such problems, a technology of using a contact or noncontact type pad shape measuring apparatus and obtaining the polishing conditions and the dressing conditions based on the measured profile of a polishing pad surface is disclosed as a conventional technology (see JP-A-2002-270556). Also, a technology of setting the angle of a dressing tool so as to perform a uniform dressing without being influenced by a polishing plate shape is disclosed (see JP-A-2004-090142).